Metabolism

Metabolism - Energy, ATP, and Enzymes

Energy Flow on Earth

• Sun: Source of energy that flows through the ecosystem.

  • Light energy is captured through photosynthesis, leading to the formation of high-energy molecules.

• Flow of Energy: Energy flows in one direction (from the sun to the universe).

Fundamental Equation

• E=mc²

  • Represents the equivalence of mass and energy.

First Law of Thermodynamics

• Energy cannot be created nor destroyed, only transformed from one form to another.

Different Forms of Energy

• Potential Chemical Energy: Energy stored within molecules.

• Kinetic Energy: Energy of motion.

• Gradient Energy: Can be chemical (ionic gradients), electrical (separated charge), or thermal energy.

• Other Forms: Mechanical energy and sound energy.

Second Law of Thermodynamics

• Spontaneous processes increase disorder/chaos or decrease order.

• Entropy (S): A measure of disorder within a system.

  • As entropy increases, disorder increases.

• Release of Heat: Cellular processes can be thought of as releasing heat to satisfy entropy requirements.

Open Systems

• Living organisms are considered open systems.

  • They extract energy from the environment to maintain order and release heat.

Cellular Work

• Cells perform various types of work that require energy:

  • Chemical Work: Involves metabolic reactions.

  • Mechanical Work: Movement and physical activities.

  • Synthesis Work: Creating complex molecules.

  • Transport Work: Moving substances across membranes.

Metabolism

• Definition: Encompasses all chemical reactions associated with life focusing on energy transformations.

Anabolic Pathways

• Function: Build complex molecules from simple building blocks.

  • Example: Photosynthesis is a synthesis reaction involving dehydration/condensation reactions to create large biological molecules.

Catabolic Pathways

• Function: Break down complex molecules into subunits, decreasing order and releasing energy.

  • Examples: Hydrolysis reactions and cellular respiration.

Gibbs Free Energy (G)

• Formula: Change in Gibbs Free Energy: \Delta G = \Delta H - T\Delta S

  • Where:

  • \Delta G = Change in Gibbs Free Energy

  • \Delta H = Change in enthalpy

  • \Delta S = Change in entropy

• Energetic Analysis:

  • Exergonic Reactions:

  • Spontaneous and energetically favorable.

  • Releases free energy in catabolic processes.

  • \Delta G is negative; reactants possess more energy than products.

  • Endergonic Reactions:

  • Not spontaneous, therefore not energetically favorable.

  • Consumes free energy in anabolic processes.

  • \Delta G is positive; products possess more energy than reactants.

Energy Coupling

• Process in which an endergonic reaction occurs simultaneously with an exergonic reaction to drive chemical work.

  • Overall, \Delta G must be negative for the reactions to proceed.

Enzymes

• Definition: Enzymes are proteins acting as biological catalysts that speed up reactions.

Active Site

• The specific region on the enzyme where the substrate binds non-covalently.

Substrate

• The reactant(s) that are altered in the reaction catalyzed by the enzyme.

Substrate Specificity

• Each enzyme typically binds and converts only a specific substrate or a closely related group of substrates.

Transition State

• The high-energy state that reactants must achieve before a reaction can occur.

Activation Energy (EA)

• The minimum amount of energy required for reactants to reach the transition state.

Enzyme/Substrate Interaction

• Occurs at the active site through various interactions:

  • Ionic interactions

  • Hydrophobic interactions

  • Hydrogen bonds

  • Van der Waals interactions

Lock and Key Model

• Concept: The enzyme and substrate fit together precisely like a key fits into a lock.

• Induced Fit Model:

  • Suggests that both the enzyme and substrate undergo conformational changes upon binding, improving their fit and facilitating catalysis.

  • This model explains how enzymes enhance their ability to lower activation energy.

Cofactors

• Helper ions or molecules that assist enzymes in catalyzing reactions.

Regulation of Enzymes

• Enzyme activity can be regulated by various factors.

Inhibitors

• Molecules that slow down or prevent enzyme activity:

  • Competitive Inhibitors: Bind to the active site, competing with the substrate and decreasing the reaction rate.

  • Noncompetitive Inhibitors: Bind to an enzyme at a site other than the active site, altering the enzyme's shape and function without competing for the active site.

Photosynthesis and Respiration

• Photosynthesis: Conversion of light energy into chemical energy by plants, algae, and bacteria.

  • General equation: 6 CO2 + 6 H2O + light \rightarrow C6H{12}O6 + 6 O2

• Respiration: The process of converting organic compounds into energy within cells, releasing carbon compounds as byproducts.